Field of the Invention
The invention pertains to methods and apparatus for drying anode and cathode materials in the fabrication of lithium ion batteries. More specifically, it pertains to methods involving the simultaneous application of microwave heating and hot air drying.
Description of Related Art
In high volume production of electrodes for lithium ion batteries drying is the highest-cost unit operation. In conventional processing, anode or cathode slurries are cast onto metal foils and dried under highly controlled conditions in very long furnaces. The furnace length (which can be ˜40 m long) is dictated by the limited rate at which water, N-methyl-2-pyrrolidone (NMP), or other selected solvent can be removed from the slurry. Higher temperature drying can increase the drying speed but can cause binder migration, surface cracking, particle segregation, orange peel defects or pore-blocking skin formation; in general, controlling these issues becomes increasingly difficult as the electrode thickness increases.
There is a need for improved drying processes to speed the drying process without creating the aforementioned defects, particularly when processing thicker electrodes.